1. Field of the Invention
The present invention generally relates to a universal serial bus (to be abbreviated as USB hereinafter) control circuit, and more particularly, to a USB control circuit with an automatic route-switching function. The USB control circuit employs an enhanced device routing controller to operate in coordination with a plurality of port routing controllers and switching devices such that the port connected with enhanced USB devices is automatically switched to the enhanced USB transceivers to be controlled by the enhanced USB host controller.
2. Description of the Prior Art
With the rapid development in the information industry, people have increasing needs for a higher operation speed as well as a higher data transmission rate of information products. Universal Serial Bus (USB) technology according to the conventional USB standard (USB 1.1) has become insufficient in many aspects.
The advantages of the USB standard include compatibility with “Plug-And-Play” (PNP), ability in connecting up to 127 different peripheral devices on the bus at a time and only one interruption request (IRQ) is required. The conventional USB standard 1.1 has been applied in variety of computer peripheral application designs, but no one has heretofore thought to use it as an interface for an image processing system. This is primarily because the conventional USB standard is much slower than the PCI or ISA buses. More particularly, the theoretical maximum bandwidth of the USB standard is 12 mega bits per second (Mbps) or 1.5 mega bytes per second (MBps), several times slower than the 8.33 MBps ISA bus and orders of magnitude slower than the 133 MBps PCI bus. And in real applications, there may has more than one device share the same USB interface, no single peripheral can expect to utilize the full range of the 1.5 MBps maximum theoretical bandwidth of the USB standard. Accordingly, USB 1.1 is not believed to be fast enough to support the data flow requirements of an image processing system.
Even though a new USB standard (USB 2.0) has recently been proposed to reach a higher data transmission rate of 480 Mbps, however, most of the peripheral devices still operate according to USB 1.1. A solution to solve the compliance problem between USB 1.1 and USB 2.0 with four USB ports is illustrated in FIG. 1. The configuration comprises: a first USB pad 121, connected to a first USB port 141; a second USB pad 123, connected to a second USB port 143; a third USB pad 125, connected to a third USB port 145; a fourth USB pad 127, connected to a fourth USB port 147; an enhanced USB host controller 13, a first USB host controller 15 and a second USB host controller 17; wherein there are an enhanced USB transceiver 16, a USB transceiver 18 and a port routing controller 19 installed in each of the USB ports 141, 143, 145 and 147.
Since the enhanced USB transceiver 16 and the USB transceiver 18 are connected to each of the USB pads 121, 123, 125 and 127, and each of the enhanced USB transceiver 16 and the USB transceiver 18 is connected to the enhanced USB host controller 13 or one of the first USB host controller 15 and the second USB host controller 17 by the port routing controller 19. In this fashion, whether the USB device (not shown) connected to a USB pad is an enhanced USB device or not can be determined by an enhanced USB device chirp sequence. Furthermore, the control over the USB pad is switched to the USB host controller or the enhanced USB host controller by the port routing controller 19, so as to achieve a higher transmission rate.
In the universal host controller interface (UHCI) specification according to USB 1.1, one host controller can only control two USB ports. Even though there is no such limit in another specification, the open host controller interface (OHCI), however, in practical cases, only three USB ports can be controlled. This results in two USB host controllers. On the other hand, an enhanced USB host controller can control a plurality of USB ports.
The prior art configuration may achieve automatic port route switching to prevent improper interconnection. However, one enhanced USB transceiver is required for each pad. Moreover, the occupied area ratio of an enhanced USB transceiver to a USB transceiver is about 10:1. The chip size of a generally utilized configuration with 6 USB ports may dramatically increase due to the enhanced USB transceiver is applied at every USB pads, and this will result in increasing fabrication cost. Furthermore, the above configuration may lead to a considerable waste of resources since there is little chance for all the USB pads to be connected with enhanced USB devices.
Accordingly, to avoid any possible waste of resources, the number of enhanced USB transceivers is designed to be less than the number of USB pads. This will limit the enhanced USB devices to be connected to some specific USB pads. Therefore, if it is not confirmed whether each of the USB pads is connected to an enhanced USB transceivers such that some enhanced USB devices are connected to the pads that are not connected to the enhanced USB transceivers, and the enhanced USB devices will not function as they are designed to.
Certainly, the enhanced USB devices is not only meaning the high speed USB devices, but also further over high speed USB devices.
Therefore, there is need in providing a USB control circuit with an automatic route-switching function, so as to overcome the problems such as waste of resources, improper interconnection and increased fabrication cost.